The Slurry (content 10 to 40% Solids depending on application) is fed into the Spiral from the top. Spread on the spiral bottom, it moves down by gravity. A transverse flow which is directed inwards on the sluice bottom or outside on the slurry surface is superimposed on the main flow.

This combination results in a separation of the particles contained in the suspension, depending on their density. Particles with a lower specific gravity, such as wood, coal or organic matter, are concentrated in the outer areas of the flow. Particles with a higher specific gravity are transported towards the spiral axis.